The present invention relates in general to remote vehicle entry systems, and more specifically to a directional antenna to establish certain reception zones for a remote vehicle entry system.
Remote entry systems are known for cars, trucks, and other transportation vehicles which operate locks anti-theft systems and vehicle personality features such as seat and mirror position. A remote entry radio receiver is mounted in the vehicle which responds to a radio transmitter carried by the user of the vehicle. In one common type of system, the user depresses a control button on the remote transmitter causing a coded signal to be transmitted to the receiver identifying a command desired by the user, e.g. lock or unlock doors, unlock trunk, or arm, disarm or trigger an anti-theft system. Unique portions of the codes identify the individual transmitter to insure that only an authorized user gains access to the vehicle. The codes may also differentiate between a plurality of authorized transmitters, each carried by a different driver of the vehicle, to allow automatic adjustment of vehicle accessories according to the preset personalities of the particular user (e.g., seat and mirror positions and radio settings).
In another type of system known as a passive entry system, communication between the transmitter and receiver occurs automatically when the portable transmitter comes within a predetermined distance of the receiver. Preferably, the receiver detects not only the presence of an authorized transmitter but also localizes the transmitter to a predetermined zone around the perimeter of the vehicle in order to only unlock an appropriate door or trunk adjacent to that zone. Such localization may also be desired is pushbutton remote entry systems.
Radio frequency (RF) communication signals are typically employed for their advantages of penetrating and passing through other objects, their low power, and their low cost. In order to differentiate between predetermined zones around the perimeter of the vehicle, a directional antenna is required to localize the RF signals from the portable transmitter. The antenna signals may also have to be processed to determine which antenna receives a stronger signal, thus localizing the transmitter.
Prior art directional antennas suffer from disadvantages of having complex shapes and large size making them difficult to package in a vehicle. It is preferable to conceal the antenna to protect it from the environment and to improve vehicle aesthetics. In order to conceal the antenna, it is usually necessary to locate the antenna beneath the sheet metal body of a vehicle. However, the sheet metal shields and adversely affects the performance of the antenna.